Previous aqueous VAc/NMA copolymer emulsions prepared in the absence of any protective colloid or surfactant required the addition of a functional monomer, for example, acrylic acid, to obtain emulsion stability and cleanliness. These emulsions, however, had undesirably high emulsion viscosities and were unsuitable as RF curable wood adhesives. To be suitable as an RF curable wood adhesive a VAc/NMA copolymer emulsion must exhibit manufacturing stability and long term viscosity stability and the polymer must be of high molecular weight and demonstrate rapid cure. To provide a wood adhesive having acceptable flow properties for machine application, the VAc/NMA copolymer emulsion should have a viscosity of 5,000 to 6,000 cps which will drop to a suitable viscosity when the acidic metal salt catalyst (aluminum chloride) is added.
Relatively stable, but difficult to prepare and reproduce, aqueous VAc/NMA copolymer emulsions were prepared using the protective colloid, polyvinyl alcohol (PVOH). The addition of a small amount of an ethoxylated nonylphenol nonionic surfactant led to emulsions that were more reproducible and approached all of the desired properties of an RF curable Type I wood adhesive but did not achieve them.